FIG. 1 is a schematic block diagram of a communication system comprising: a host terminal 2 such as a desktop computer, laptop computer, tablet style computer or mobile phone; a wireless cellular modem 4 comprising an antenna 5; a mobile cellular network 6 such as a 3GPP network comprising one or more access point nodes 12 (APNs) coupled to a plurality of antennas 10; and a further, packet-based network 8 such as the Internet comprising a plurality of areas 14 and routers or gateways 16. The system allows the host terminal to access the Internet 8, e.g. using Internet Protocol version 6 (IPv6) and/or Internet Protocol version 4 (IPv4).
The modem 4 is connected or connectable to the host terminal 4 by means of a first link. The modem is connected or connectable to the 3GPP network 6 or other such cellular network by means of a second connection 20. The second connection connects via an antenna 18 to an access point node (APN) of the cellular network 6. Each of the one or more access point nodes 12 connects on to a respective gateway 16 of the Internet 8. The host terminal 2 is installed with one or more applications 18 which when executed on the host terminal 2 send and/or receive communications over the Internet 8 via the first and second links.
The first connection, between the host and modem, comprises a physical connection and a link protocol that drives the physical connection. The physical connection could be for example a wired connection such as USB, an infrared connection, or a radio frequency connection such as Bluetooth. The link protocol is the protocol that operates at the link layer, i.e. which handles the transfer of data to or from just the next physical node (as opposed for example to internet layer protocol which routes across multiple nodes, or transport layer protocol which is concerned with end-to-end communication issues). For the purpose of link layer transmission, devices such as routers and gateways 16 and host terminals 4 may be allocated a physical identifier which may be referred to as a link layer address (LLA). The LLA or link-layer address is the unique link address of a device connected to a packet-based network 8 such as an IPv6 network.